Makes GET /metrics work regardless of the value of the Host header.
This was not possible before 220468f7a103 which added the ability to
have global HTTP modules, which was partly why the per-host part was
kept while the module lived among the community modules.
Another reason was to provide some semblance of security by obscurity by
only loading the module on e.g. a 'localhost' VirtualHost or Component.
The new IP limits obsoletes this.
This version has several changes from the earlier mod_prometheus:
- Conversion of metrics into the text-based OpenMetrics format is moved to
util.openmetrics
- Support for IP-based access control
- Compatibility with earlier Prosody versions removed